Vapor liquid solvent extraction process



A08 22, 1950 H. J. HIBsHMAN r-:TAL 2,520,006

VAPOR LIQUID SOLVENT EXTRACTION PROCESS l Filed Oct. 11. 1944 Conba-usa.

5- .r9 1 Ao 45 I 4s 44 ==l SEDAN-rm?. l 44. APK-:IIL f Le Towewr-Z-:I- L 4'? 49 AfL-:3::

Eq Clbborneq Patented ug. 22, 19,50

VAPOR LIQUID SOLVENT EXTRACTION PROCESS i Henry J. Hibshman, Plainfield, and Robert H. Latferty, Bradley Beach, N. J., assignors to Standard 4Oil Development YCompany, a corporation of Delaware Application October 11, 1944, Serial No. 558,260

4 Claims. (Cl. 21R-39.5)

This invention relates to the solvent treatment of mineral oil and especially to the recovery of the solvent from an overhead vapor when vaporliquid extracting a petioleum fraction using a solvent having a boiling range within about 150 F. of the boiling range of the mineral oil being extracted.

In the treatment of mineral oils it is common to concentrate desirable constituents or remove undesirable impuritiesfrom the oil by the use of various selective solvents. It has been common to use either of two methods for accomplishing the extraction. In the first, the liquid oil is treated countercurrently with a liquid solvent to produce a raflinate rich in the more paraflinic constituents and containing relatively small amounts of solvent, and an extract phase containing the more aromatic constituents dissolved in a relatively large amount of solvent. In this process as normally carried out on lubricating oils, the boiling point of the solvent is usually at least 200 or 300 F. lower than the petroleum fraction being treated and is easily removed from the extract and raflinate by distillation. The extraction of lubricating oils using phenol, furfural and chlorex are examples of such extractions.

The second process for the treatment of petroleum fractions with selective solvents involves introduction of the liquid solvent into one end of a, treating system into the center of which the petroleum fraction is introduced, usually in a wholly or partially vaporized state. The petroleum vapor passes countercfurrently to the solvent. The more aromatic or hydrogen-deficient constituents are concentrated in the liquid solvent phase while the more parainic or hydrogen-rich constituents are concentrated in the vapor phase. A portion of the hydrocarbons dissolved in the solvent is revaporized at the extract end of the unit to produce hydrocarbon vapors in this section of the unit thereby eiecting further purication of the aromatic constituents. Since in such a process it is common to use solvents boiling within about 200 F. of the boiling range of the petroleum fraction being treated, the raffinate phase usually contains a considerable quantity of solvent which is often relatively diflicult or impossible to remove by simple distillation. Examples oi this second procedure for solvent extracting petroleum fractions are as follows: (1) the extraction of toluene from virgin cracked and hydroformed naphthas using solvents such as phenol, methylethyl ketone, and methyl alcohol, and (2) the extraction of isoprene and n-butylenes using acetone as a selective solvent.

The recovery of solvent from the products of this second method of solvent treating petroleum fractions is the subject of this patent application. It has been found that the solvent loss in the extractor overhead can be appreciably reduced by the injection into the top of the extractor oi relatively small quantities of a second solvent which is completely or at least partially miscible with the rst solvent |but relatively insoluble in the petroleum fraction being treated. In the preferred method of recovering solvent, the secondary solvent boils from 25 to 200 F. lower than the petroleum fraction being treated. In this case the secondary solvent is revaporized in the raffinate end of the treating zone and appears with the rafiinate from which it is separated by decantation and recycled to the treating zone, It has been found that when operating in this marier the solvent loss with the rainate is reduced to from 1/2 to 115 the loss without injecting a secondary solvent.

As an example of this process, it has been found that when vapor liquid extracting toluene from a V-250 F. boiling range, hydroformed naplitha containing 21% toluene rising phenol in the ratio of 300 parts phenol to parts naphtha feed and a reflux ratio of 1/1 with 10 plates above the phenol feed point, that the raffinate contains 1.5# phenol/bbl. of ranate. When 9 vol, percent water is injected into the top of the extraction tower while using only a 1/3 reux ratio, the phenol content of the raffinate is reduced to 0.2# phenol/bbl. of rafnate.

More generally, about 6 to 12 volume percent of water may be employed in toluene extraction processes of this character. In the case in which phenol is employed for the vapor liquid extraction of Xylenes, the amount of water employed is about 25-41 volume percent based upon the volnime of hydrocarbons withdrawn as an overhead product. The specified amount of water is the quantity required to form constant boiling mixtures between the water and the overhead hydrocarbon products.

This invention will be more clearly understood on reading the following description with reference to the attached drawing. Reference numeral I designates an extraction tower provided with perforated plates 2 and a steam coil 3 in the bottom to regulate the temperature. The naptha to be extracted is introduced by means of pipe 4 to the center of the extraction section, below the point where the primary solvent is injected. The naphtha is introduced into the tower in the vapor state. Phenol, liquid phenol in this case. is introduced about one-third down from the top of the tower through pipe 5 and flows in countercurrent flow to vapors of the naphtha rising upwardly through the tower. It is not intended to limit this invention to the extraction of toluene and xylene or to specify the solvent named as other mixtures may be extracted with the use of other solvents such as cresols methylethyl ketone, furfurol, acetone, etc. Phenol owing downward- 1y through the tower is separated with dissolved ingredients by means of solvent recovery pipe 6 provided with valve `I. The vapors rising upwardly through the tower are removed by means of pipe 8 and passed through condenser 9. A condensate passes through pipe I to settler II where a separation of the mineral oil from water which is also present is obtained. A raflinate oil may be passed by means of pipe I2 provided with valve I3 to the upper part of the tower as a reux to eil'ect more eiilclent separation of the mixture. The remaining part of the raffinate that is not used as a reiiux is removed through pipe I4 provided with valve I5. 'Ihe water is removed from the settler II by means of pipe I6, provided with valve II, and is returned to the upper plates of the extraction tower. The plates upon which this water is reuxed are the upper plates preferably the top plate along with the reiluxed oil. However, it is permissible to introduce the water on or even below the phenol feed plate. The excess water may be removed by means of pipe I8 provided with valve I9 and if sumcient water is not present, fresh water may be introduced by means of this pipe I8. The water which was removed through pipe l was vaporized within the column and in so doing condensed an amount of hydrocarbon proportional to the respective heats of vaporization (vaporization of 1 liquid volume of water serves to condense about 10 liquid volumes of hydrocarbon).

Thequantity of water recycled is critical and is controlled by tower temperatures which are sensitive to the presence of small traces of water. In the foregoing example, when less than about 9 vol. per cent of water based on the overhead is used at a reflux ratio of 1 to 3, all of the water is vaporized in the upper part of the tower. In such cases the temperature of the phenol feed plate does not drop from the conventional operating temperature of about 234 F. and the phenol loss is high. When appreciably more than about 9 vol.

per cent water is used all the temperaturesV throughout the extractor drop sharply from about 234 F. to 195-205 F. 'I'hese figures are obtained when taking a 75% overhead yield to produce a 95% recovery of nitration grade toluene on a naphtha cut having a boiling range ranging from 1'I5-260 F. and containing 25% toluene and the amount of the solvent Aused is 300 vol. per cent phenol and 10 plates are in the tower above the phenol feed plate. Where such a sharp drop in extractor temperatures, that is from 234 F. to 205 F., is obtained all of the water is not revaporized, some passing out the bottom of the tower, and the phenol loss in the railinate is relatively high. When the water rate is controlled to maintain the temperature on the rst few plates below the phenol feed at about 210 F. and the remaining lower plates at about 234 F., that is by using about 9 vol. per cent water, all of the water is again revaporized and appears with the overhead. In this case, the phenol loss is at a minimum as shown by the following data obtained when operating with a reilux ratio of 1 to 3.

TABLE I Water injected, vol. per cent on overhead product O 9 28 Phenol in railinate, #/bbl 2 0.2 3.0

As shown in the following table, the use of 9% water injection with 10 plates reduces the phenol loss to the loss with no water injection.

TABLE Il Phenol loss vs. plates No. of plates above phenol feed 4 Phenol in railinate, #/.bblx

No water injection, (1:1 external R. R.) 2.5 1.5 1.2 Water injection, 9 v01. per cent on overhead (1:3 external R. R.) 0.8 0.2

scribed for recovery of solvent from the extrac tor overhead.

While the above specifications disclose the general principles involved in this invention, what we claim specifically is as follows:

1. In the process for extracting from a mineral oil a compound selected from the group consisting of toluene and xylenes in which vapors of mineral oil are introduced to a tower and liquid phenol is introduced to the tower above the point of mineral oil introduction, the improvement which consists of introducing liquid water to the upper part of the tower above the point of phenol introduction, said water being introduced in a quantity within the range of 6 to 41 volume percent based upon the volume of hydrocarbons withdrawn as overhead product to form a constant boiling mixture with the hydrocarbons withdrawn overhead and said quantity being such that liquid water passes downwardly in the tower but is vaporized before reaching the bottom of the tower.

2. The process for extracting toluene from mineral oil in which vapors of mineral oil are introduced to a tower and liquid phenol is introduced to the tower above the point of mineral oil introduction, the improvement which consists of introducing liquid water to the upper part of the tower above the point of phenol introduction, said water being introduced in a quantity within the range of 6 to 12 volume percent based upon the volume of hydrocarbons withdrawn as overhead product to form a constant boiling mixture with the hydrocarbons withdrawn overhead and said quantity being such that liquid water passes downwardly in the tower but is vaporized before reaching the bottom of the tower.

3. The process for extracting toluene from mineral oil in which vapors of mineral oil are introduced to a tower and liquid phenol is introduced to the tower above the point of mineral oil introduction, the improvement which consists of introducing liquid water to the upper part of the tower above the point of phenol introduction, said water being introduced in a quantity of about 9 volume percent based upon the volume of hydrocarbons withdrawn as overhead product to form a constant boiling mixture with the hydrocarbons withdrawnoverhead and said quantity' being such that liquid water passes downwardly in the tower but is vaporized before reaching the bottom of the tower.

4. The process for extracting xylenes from minerai oil in which vapors of`minera1 oil are introduced to a tower and liquid phenol is in troduced to the tower above the point of mineral oil introduction, the improvement which consists oi introducing liquid water to the' upper part of the tower above the point of phenol introduction. said water being introduced in alquantity within the range of 25 to 41 volume percent based upon the volume of hydrocarbons withdrawn as overhead product to form a constant'boiling mixture with the hydrocarbons withdrawn overhead and said quantity being such that liquid water passes downwardly in the towerbut is vapormed before reaching the bottom of the tower.

HENRY J. HIBSHMAN/v ROBERT H. REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS 

1. IN THE PROCESS FOR EXTRACTING FROM A MINERAL OIL A COMPOUND SELECTED FROM THE GROUP CONSISTING OF TOLUENE AND XYLENES IN WHICH VAPORS OF MINERAL OIL ARE INTRODUCED TO A TOWER AND LIQUID PHENOL IS INTRODUCED TO THE TOWER ABOVE THE POINT OF MINERAL OIL INTRODUCTION, THE IMPROVEMENT WHICH CONSISTS OF INTRODUCING LIQUID WATER TO THE UPPER PART OF THE TOWER ABOVE THE POINT OF PHENOL INTRODUCTION, SAID WATER BEING INTRODUCED IN A QUANTITY WITHIN THE RANGE OF 6 TO 41 VOLUME PERCENT BASED UPON THE VOLUME OF HYDROCARBONS 